Stents may be inserted into an anatomical vessel or duct for various purposes. Stents may maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Other stents may be used in different procedures in conjunction with a graft material to form a stent-graft, for example, to hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be either self-expanding or balloon-expandable, or they can have characteristics of both types of stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires and/or releasing diameter reducing ties. In a stent made of a shape memory alloy such as nitinol, the shape-memory alloy may be employed to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its predeployment configuration.
With balloon-expandable stents, the stent may be delivered and deployed using a catheter having proximal and distal ends and one or more balloons disposed on the catheter. The stent may be coupled to the balloon during insertion until the target site is reached, and then deployed by inflating the balloon to expand the stent to bring the stent into engagement with the target site. Alternatively, the stent may be placed separately in the vessel and a subsequent catheter having an expansion portion may then be inserted into the stent to expand the stent at the target site.
When stents are employed as part of a stent-graft, the stent commonly is attached to the graft using one or more sutures. Typically, the sutures are hand-sewn around the stent and directly through the graft at multiple locations to secure the stent to the graft. Such suturing techniques may be labor intensive. Further, the formation of suture holes in the graft may increase the risks of leakage through the graft, particularly since the size of such suture holes may increase over time.
Current stent-fabric attachment techniques include either tack stitching or a running stitch that follows the stent. At each stitch point, a puncture hole is made in the fabric, one on either side of the stent wire. Having suture holes presents more opportunities for fluid leakage through the graft fabric. Furthermore, cinching the stitch pulls the fabric around the stent. If the fabric is not stretchable, tightening the suture pulls the thread to one side of the puncture hole, opening it up and potentially increasing the risk of leakage.
Another difficulty with current manufacturing techniques is that they require a pattern to be drawn on the graft fabric to indicate where stents are placed during hand stitching of the stents. Drawing or marking has the potential to contaminate or damage graft fabric. Hand-stitching to a pattern also is associated with human error and increased variance in manufacturing tolerances. A method of automating the stitching process would eliminate the need to mark up the fabric and would reduce manufacturing tolerances.
Thus, there is a need for improved techniques and methods for attaching graft material to a stent without the problem of creating holes in the graft fabric and the difficulty with marking up stain-resistant fabrics.